1. Field of the invention
The present invention relates to a power supply system using an assembled battery in which storage elements are combined in series with one another, and in particular to a technique in which electric power is supplied to an assembled battery, supervisory device which watches or supervises an assembled battery, with a simple structure or arrangement.
2. Description of the Related Art
In the past, there have been developed techniques with respect to an assembled battery, which can increase an amount of electric energy able to be stored or charged, and at the same time reduce the loss at the time of charging and discharging, by combining storage elements in series with one another. Such an assembled battery is provided with an assembled battery supervisory device for the purpose of supervising the states of charge of the storage elements which constitute the assembled battery.
In a power supply system using such a kind of assembled battery, in cases where the electric power required for the operation of the assembled battery supervisory device is obtained from the assembled battery, the voltage of the assembled battery is generally different from an operating voltage required by the assembled battery supervisory device, and so stable electric power is supplied to the assembled battery supervisory device through the use of a regulator (voltage conversion circuit).
For example, as a conventional power supply system for use with a vehicle, there has been known a technique in which large electric power can be supplied to the vehicle by connecting a plurality of storage elements in series with one another (for example, refer to an under-mentioned first patent document).
In the invention disclosed in the first patent document, in order to eliminate variation in voltage of the individual storage elements occurring due to the individual variation of the storage elements at the time when the storage elements are connected in series with one another thereby to supply electric power to the vehicle, a balance circuit (cell balancer) is attached to the storage elements, and is driven to operate in an intermittent manner during the stop of the vehicle, so that the voltage balance of the storage elements is made constant.
FIG. 9 is a block diagram showing a conventional power supply system using an assembled battery disclosed in the first patent document, wherein there is shown an arrangement in which a power supply for a assembled battery supervisory device 2 is obtained from an assembled battery 1.
In FIG. 9, the conventional system is provided with the assembled battery 1 that is composed of storage elements connected in series with one another, the assembled battery supervisory device 2 that serves to supervise or monitor the assembled battery 1 and to balance (equalize) the voltages of the storage elements, an electricity storage unit 101 that is composed of a vehicle mounted battery, an alternator 102 and a DC-DC converter 103 that are connected to the assembled battery 1 and the assembled battery supervisory device 2, and an electric load 104 that is connected to the electricity storage unit 101 and the DC-DC converter 103.
The assembled battery supervisory device 2 is provided with a voltage conversion circuit 21 that stabilizes the voltage from the assembled battery 1 to a desired voltage, a cell balancer 23 that balances or equalizes the voltages of the storage elements of the assembled battery 1, an insulating communication circuit 30 for communicating with external vehicle mounted equipment (not shown), and an internal arithmetic device 22 that calculates an amount of drive of the cell balancer 23 and at the same time provides a communication instruction to the insulating communication circuit 30.
The assembled battery 1 is supplied with electric power from the alternator 102, and the DC-DC converter 103 converts the electric power from the assembled battery 1, and supplies the electric power thus converted to the electric load 104 and the electricity storage unit 101.
In the case of the conventional system (FIG. 9) disclosed in the first patent document, when the number of the storage elements which are connected in series with one another in the assembled battery 1 increases, an input voltage to the voltage conversion circuit 21 in the assembled battery supervisory device 2 becomes a higher voltage, and hence, it will be necessary to use elements with high operation guarantee voltage as the voltage conversion circuit 21, thus giving rise to an enlargement and a cost rise of the structure or arrangement.
In addition, as another conventional system, there has been known an arrangement in which electric power for an assembled battery supervisory device 2 is obtained from an electricity storage unit 101, as shown in FIG. 10.
In FIG. 10, the assembled battery supervisory device 2 is provided, in place of the above-mentioned voltage conversion circuit 21 (refer to FIG. 8), with an insulating voltage conversion circuit 20 for electrically insulating a high voltage system and a low voltage system from each other for the purpose of preventing electric leakage.
The insulating voltage conversion circuit 20 converts the electric power supplied from the electricity storage unit 101 by means of an isolation transformer, and supplies the electric power thus converted to an internal arithmetic device 22 and an insulating communication circuit 30.
In the case of the conventional system shown in FIG. 10, the insulating voltage conversion circuit 20 is required, which has become a cause for the enlargement and the cost rise of the arrangement or structure.
As another conventional system, there has also been proposed a technique in which in an electricity storage module that is composed of storage elements connected in series with one another, it is made possible to supply electric power to electrical and electronic equipments or the like which are different in operating voltage from one another, by supplying electric power from a center tap of an electricity storage module to the electrical and electronic equipments or the like, without using a DC-DC converter (for example, refer to an under-mentioned second patent document).
In the conventional system disclosed in the second patent document, it is constructed such that the electric power for the electrical and electronic equipments is obtained from the center tap of the assembled battery in which the storage elements are connected in series with one another, and a balance circuit is driven so as to make the voltages of the storage elements, which constitute the assembled battery, equal to one another.
In the case of the conventional system disclosed in the second patent document, the voltages of the storage elements are made equal during the use or operation of the assembled battery, but in cases where there is variation in the internal resistances of the individual storage elements which constitute the assembled battery in the course of using the assembled battery, there will also be variation in the terminal voltages of the storage elements resulting from the difference of the internal resistances thereof. As a result, there will be a possibility that the states of charge of the storage elements may not be able to be made equal to one another in a correct manner.
Then, in cases where the states of charge of the storage elements can not be made equal to one another, it is necessary to continue the driving of the assembled battery supervisory device in order to equalize the difference of the states of charge of the storage elements after the use or operation of the assembled battery is terminated, so that the electric power consumption will be increased after the termination of the use or operation of the assembled battery.
As a result, in cases where this conventional system has been applied as a power supply system for a vehicle, there has been a possibility that the electric power consumption after the stop of the vehicle may be increased.